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Nervous, Sensory, and Locomotor Systems
An Overview of animal Nervous Systems
The Human Nervous System: A Closer Look
The Senses
Locomotor Systems
The nervous system is our communication system
between our brain and our internal and external
worlds.
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Biology and Society:
Beyond Human Experience
• Many animals perceive the world in ways we cannot.
• Bats and porpoises generate ultrasonic sounds in echolocation to
– Detect echoes
– Determine the size, shape, location, speed, and direction of objects in
the environment
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Figure 27.00
• Many species of fish use electroreception to generate weak
electric fields that reveal objects in low-visibility environments.
• Migratory birds, fish, turtles, amphibians, and bees use
magnetoreception to
– Detect magnetic fields
– Orient their movements relative to Earth’s magnetic fields
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AN OVERVIEW OF ANIMAL NERVOUS SYSTEMS
• The nervous system forms a communication and coordination
network throughout an animal’s body.
• Neurons are nerve cells specialized for carrying electrical signals
from one part of the body to another.
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Organization of Nervous Systems
• The nervous system of most animals has two main divisions.
– The central nervous system (CNS) consists of the brain and spinal cord
(in vertebrates).
– The peripheral nervous system (PNS) consists of mostly of nerves that
carry signals into and out of the CNS.
– A nerve is a communication line made from cable-like bundles of neuron
fibers.
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• The three interconnected functions of the nervous system are
carried out by three types of neurons:
– Sensory neurons function in sensory input
– Interneurons integrate information
– Motor neurons function in motor output
• Effectors perform the body’s responses to motor output.
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SENSORY INPUT
Sensory receptor
Sensory
neuron
MOTOR OUTPUT
Motor
neuron
Effector cells
Peripheral nervous
system (PNS)
INTEGRATION
Interneuron
Brain and spinal cord
Central nervous
system (CNS)
Figure 27.1
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Neurons
• Neurons are cells of the nervous system and are similar to
electrical wires
– Are the functional units of the nervous system
– Vary widely in shape
– Share some common features
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Signal
direction
Dendrites
Cell
body
Axon
Supporting cell
Signal
pathway
Synaptic
terminals
Nucleus
Myelin sheath
Figure 27.2
• Two types of extensions project from the cell body:
– Dendrites, which:
–
Receive incoming messages from other cells
–
Convey the information toward the cell body
– Axons, which transmit signals toward another neuron or toward an
effector
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• Supporting cells – called glial cells
– Outnumber neurons by as many as 50 to 1
– Protect, insulate, and reinforce the neurons
• The myelin sheath
– Forms an insulating material around an axon
– Helps increase the speed of the electrical signal
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• An axon ends in a cluster of branches, each with a bulb-like
synaptic terminal that relays signals to
– Another neuron or
– An effector
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Signal
direction
Know this!
Dendrites
Cell
body
Axon
Supporting cell
Signal
pathway
Synaptic
terminals
Nucleus
Myelin sheath
Figure 27.2
Incoming signal
Dendrites Cell
body
Myelin
Axon
(speeds signal
transmission)
Synaptic terminal
Figure 27.UN05
Sending a Signal through a Neuron
• A resting neuron has potential energy that can be put to work to
send nerve signals from one part of the body to another.
• This difference in charge (voltage) across the plasma membrane
of a resting neuron is the resting potential.
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The Action Potential
• A stimulus is any factor that causes a nerve signal to be
generated.
• A stimulus of sufficient strength can trigger an action potential, a
nerve signal that carries information along a neuron.
Action Potential
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Propagation of the Signal
• An action potential is a localized electrical event.
• To function as a nerve signal over a distance, this local event
must be passed along the neuron.
• Action potential propagation is like a “domino effect” along a
neuron.
– All-or-none events
– The same no matter how strong or weak the stimulus that triggers them
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Passing a Signal from a Neuron to a Receiving Cell
• A synapse is a relay point
– Between two neurons or
– Between a neuron and an effector cell
• Synapses come in two varieties:
– Electrical
– Chemical
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• Chemical synapses
– Have a narrow gap, the synaptic cleft, separating a synaptic terminal of
the sending neuron from the receiving cell
– Rely on neurotransmitters, chemicals that carry information from one
nerve cell to another kind of cell
The Synapse
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Synaptic
terminal of
sending
neuron
Dendrite of
receiving neuron
SYNAPSE
Sending neuron
Action
potential
arrives.
Vesicles
Neurotransmitter
Synaptic
terminal
Receptor
Ions
Vesicle fuses
with plasma
membrane.
Neurotransmitter
is released into
synaptic cleft.
Synaptic
cleft
Neurotransmitter
binds to receptor.
Receiving
neuron
Ion channels
Ion channel opens and
triggers or inhibits a
new action potential.
Ion channel closes.
Neurotransmitter is
broken down and
released.
Neurotransmitter
molecules
Figure 27.5
Dendrites
Myelin
sheath
Receiving
cell body
Axon
SEM
Synaptic
terminals
Figure 27.6
Neurotransmitters
• A variety of small molecules can act as neurotransmitters:
– Amines, derived from amino acids that affect sleep, mood, attention,
and learning
– Peptides, short chains of amino acids that include endorphins, which
decrease pain perception
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Drugs and the Brain
• Many drugs, such as caffeine, nicotine, and alcohol, act at
synapses by increasing or decreasing the normal effect of
neurotransmitters.
• Prescription drugs used to treat psychological disorders alter the
effects of neurotransmitters.
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THE HUMAN NERVOUS SYSTEM:
A CLOSER LOOK
• Although there is remarkable uniformity in the way nerve cells
function, there is great variety in how nervous systems as a
whole are organized.
• Vertebrate nervous systems are diverse in
– Structure
– Level of sophistication
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The Central Nervous System
• Vertebrate central nervous systems
– Integrate information coming from the senses
– Transmit signals that produce responses
– Consist of the
–
Brain, the master control center of the nervous system
–
Spinal cord, a jellylike bundle of nerve fibers inside the spinal
column
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Central nervous
system (CNS)
Brain
Spinal cord
Peripheral nervous
system (PNS)
Figure 27.7
BRAIN
Forebrain
(sophisticated
integration)
 Thalamus
 Hypothalamus
 Cerebrum
Midbrain
Hindbrain
 Pons
 Medulla oblongata
 Cerebellum
(coordinates
movement)
Brainstem
(filters motor and
sensory input)
Figure 27.UN07
• The brain and spinal cord
– Contain spaces
– Are filled with cerebrospinal fluid, a liquid that
–
Cushions the CNS
–
Helps supply the CNS with nutrients, hormones, and white blood
cells
• Also protecting the brain and spinal cord are layers of connective
tissues called meninges.
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Brain
Cerebrospinal fluid
Meninges
Spinal cord
(cross section)
Spinal cord
Figure 27.8
The Peripheral Nervous System
• The vertebrate peripheral nervous system is divided into two
functional components:
– The somatic nervous system
– The autonomic nervous system
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PERIPHERAL NERVOUS SYSTEM
Somatic nervous system
(voluntary)
Autonomic nervous system
(involuntary)
 Parasympathetic division
LM
(rest and digest)
 Sympathetic division
(fight or flight)
Voluntary leg muscles
Involuntary heart muscle
Figure 27.9
• The somatic nervous system
– Carries signals to and from skeletal muscles
– Mainly responds to external stimuli
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• The autonomic nervous system
– Regulates the internal environment
– Controls
–
Smooth and cardiac muscles
–
Organs and glands of the digestive, cardiovascular, excretory, and
endocrine systems
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• The autonomic nervous system contains two sets of neurons with
opposing effects on most organs:
– The parasympathetic division primes the body for digesting food and
resting.
– The sympathetic division prepares the body for intense, energyconsuming activities.
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The Human Brain
• The brain, the most sophisticated computer, consists of
– Up to 100 billion intricately organized neurons
– Many more supporting cells
• The brain is divided into three regions:
– The hindbrain
– The midbrain
– The forebrain
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Cerebrum
Forebrain
Cerebral
cortex
Thalamus
Hypothalamus
Know this!
Pituitary
gland
Midbrain
Pons
Spinal cord
Hindbrain
Medulla
oblongata
Cerebellum
Figure 27.10
Table 27.1
• The brainstem
– Consists of the hindbrain (medulla oblongata and pons) and the
midbrain
– Serves as a sensory filter, selecting which information reaches higher
brain centers
• The cerebellum, another part of the hindbrain, is a planning
center for body movements.
• The forebrain contains the most sophisticated integrating centers
in the brain:
– The thalamus, which relays information to the cerebral cortex
– The hypothalamus, with many regulatory functions
– The cerebrum, the largest and most sophisticated part of the brain
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The Cerebral Cortex
• The cerebrum consists of right and left cerebral hemispheres
interconnected by the corpus callosum.
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Left cerebral
hemisphere
Right cerebral
hemisphere
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Corpus
callosum
Thalamus
Cerebellum
Medulla oblongata
Figure 27.11
• The cerebral cortex
– Is a highly folded layer of tissue that forms the surface of the cerebrum
– Helps produce our most distinctive human traits
• The right and left cerebral hemispheres
– Have four lobes
– Are specialized for different mental tasks in a phenomenon known as
lateralization
• Higher mental activities occur in association areas of the brain.
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Frontal lobe
Frontal
association
area
Speech
Taste
Parietal lobe
Somatosensory
association
area
Reading
Speech
Hearing
Smell
Auditory
association
area
Visual
association
area
Vision
Temporal lobe
Occipital lobe
Figure 27.12
Oops!
Figure 27.13
Brain Trauma
• In 1848, a railroad accident to a man named Phineas Gage
– Propelled a three-foot-long spike through his head but
– Caused significant changes in his personality.
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Figure 27.14
Neurological Disorders
• Neurological disorders can also affect brain function.
– Major depression is extreme and persistent sadness and loss of interest
in pleasurable activities.
– Bipolar disorder involves extreme mood swings.
– Alzheimer’s disease causes mental deterioration.
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Depressed person
Area of decreased
brain activity
Healthy person
Figure 27.15
THE SENSES
• Sensory structures
– Gather information - This is how any organism detects information from
the outside world to integrate it into the brain (if present) and determine
if a response is necessary.
– It is essential for homeostasis
• Sensory transduction is the conversion of a stimulus signal to an
electrical signal by a sensory receptor cell.
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Sensory Transduction
• Receptor potentials
– Are changes in membrane potentials caused by sensory stimuli
– Vary in intensity, depending on the strength of the stimulus
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Receptor
Sugar
molecule
(stimulus)
Membrane
of sensory
receptor cell
Signal
transduction
pathway
Ion
channels
Sugar
molecule
Taste
bud
Sensory
receptor
cells
Sensory
receptor
cell
Ion
Receptor
potential
Neurotransmitter
Sensory neuron
Sensory neuron
Action potential
(to brain)
Figure 27.16
• Sensory adaptation
– Causes some sensory receptors to be less sensitive when they are
stimulated repeatedly
– Keeps the body from continuously reacting to normal background stimuli
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Types of Sensory Receptors
• Sensory receptors can be grouped into five categories, which
work in various combinations to produce the five human senses.
• A section of human skin reveals why the surface of our body is
sensitive to such a variety of stimuli.
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• Pain receptors respond to stimuli causing injury or disease.
• Thermoreceptors detect heat or cold.
• Mechanoreceptors are stimulated by various forms of
mechanical energy.
• Chemoreceptors respond to chemicals in the external
environment or body fluids.
• Electromagnetic receptors are sensitive to energy of various
wavelengths, including light.
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Vision
• Human eyes are able to
– Detect a multitude of colors
– Form images of faraway objects
– Respond to minute amounts of light energy
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Structure of the Human Eye
• The human eye consists of
– A tough outer covering, the sclera
– A transparent cornea in front of the lens
– An iris with a center opening, the pupil
– The retina, at the back of the eyeball, where photoreceptors respond to
light
• Two fluid-filled chambers make up the bulk of the eye.
– The large chamber is filled with vitreous humor.
– The small chamber contains aqueous humor.
• The optic nerve connects the retina to the brain
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Know this!
Sclera
Choroid
Muscle
Retina
Ligament
Cornea
Iris
Optic nerve
Pupil
Aqueous
humor
Lens
Vitreous humor
Blind spot
Figure 27.18
Photoreceptors
• The human retina contains two types of photoreceptors.
– Rods:
–
Are extremely sensitive to light
–
Perceive only shades of gray
–
Are distributed at the outer edges of the retina
– Cones:
–
Are less sensitive to light
–
Perceive colors
–
Are distributed at the center of focus on the retina
• Rods and cones detect light using an array of membranous disks
containing visual pigments.
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Rod
Cell body
Membranous disks
containing visual pigments
Cone
Synaptic terminals
Figure 27.20
Vision Problems and Corrections
• The most common visual problems are
– Nearsightedness, the inability to focus on distant objects
– Farsightedness, the inability to focus on near objects
– Astigmatism, blurred vision caused by a misshapen lens or cornea
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Hearing
The Structure of the Human Ear
• The ear is composed of
– The outer ear
– The middle ear
– The inner ear
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Outer ear
Know this!
Inner ear
Middle ear
Pinna
Auditory
canal
(a) Ear structure
Eardrum
Eustachian tube
Stirrup
Skull bones
Anvil
Hammer
Auditory
nerve,
to brain
Eardrum
Eustachian tube
Cochlea
(b) The middle and inner ears
Figure 27.23
Outer ear
Middle ear
Eardrum
Bones
Inner ear
Organ of Corti
(inside cochlea)
Figure 27.UN09
• The outer ear
– Consists of the pinna and the auditory canal
– Collects sound waves
– Passes sound waves to the eardrum, a sheet of tissue that separates the
outer ear from the middle ear
• In the middle ear, the vibrating eardrum passes the sound waves
to three small bones that relay the sound to the inner ear.
• The Eustachian tube
– Conducts air between the middle ear and back of the throat
– Allows air pressure to stay equal on either side of the eardrum
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• The inner ear consists of fluid-filled channels in the bones of the
skull.
• One of the channels, the cochlea, contains the organ of Corti,
which
– Is the actual hearing organ
– Includes hair cells, the receptor cells of the ear
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Function of the Human Ear
• When we hear, sound waves
– Are collected by the outer ear
– Are transmitted indirectly to the cochlea, which causes
–
Hair cells in the organ of Corti to bend
–
Nerve cells to send signals to the brain
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Outer ear
Auditory
canal
Eardrum
Hammer,
anvil, stirrup
Inner ear
Cochlea
Pressure
Pinna
Middle ear
Amplitude
One
vibration
Concentration
in middle ear
Organ
of Corti
stimulated
Time
Figure 27.25
• Louder sounds cause
– Greater movement of the hair cells
– More action potentials
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Hearing Problems
• Deafness, the loss of hearing, can be caused by
– Middle ear infections
– Injury, such as a ruptured eardrum
– Overexposure to loud noises
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MOTOR SYSTEMS
• Movement
– Is one of the most distinctive features of animals
– Relies upon an interplay of organ systems
• The nervous system issues commands to the muscular system.
• The muscular system exerts the forces that make animals move
by acting on the skeletal system.
• Actually, other than thinking, the only thing the brain can do is
send motor commands which is (are) action potentials to
muscles, to make them contract!
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The Skeletal System
• The skeletal system provides
– Anchoring
– Support
– Protection of internal organs
• All vertebrates have an endoskeleton, situated among soft
tissues, and consisting of
– Bones, hard supporting elements
– Cartilage at points of flexibility
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Know this!
Skull
Shoulder
girdle
Clavicle
Scapula
Sternum
Ribs
Humerus
Vertebra
Ulna
Radius
Pelvic girdle
Carpals
Metacarpals
Phalanges
(curled under)
Femur
Patella
Tibia
Fibula
Tarsals
Metatarsals
Phalanges
Figure 27.26
• The axial skeleton
– Supports the axis of the body
– Includes the skull, vertebral column, and rib cage
• The appendicular skeleton is made up of the bones of the
– Limbs
– Shoulders
– Pelvis
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• Much of the versatility of our skeleton comes from three types of
movable joints:
– Ball-and-socket joints in the shoulder and hip
– Hinge joints that permit movement in a single plane
– Pivot joints that allow rotation
• The bones of the skeleton are held together at movable joints by
strong fibrous ligaments.
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JOINTS
Ball-and-socket
(example: shoulder)
Head of
humerus
Hinge
(example: elbow flexing)
Pivot
(example: elbow rotation)
Humerus
Ulna
Scapula
Radius
Ulna
Figure 27.27
The Structure of Bones
• Bones
– Are covered with a connective tissue membrane
– Have cartilage at their ends that cushions the joints
– Are served by blood vessels and nerves
• The central cavity of a long bone contains yellow bone marrow,
which is mostly stored fat.
• The end of a long bone contains red bone marrow, a specialized
tissue that produces blood cells.
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Know this!
Cartilage
Spongy bone
(contains red
bone marrow)
Compact bone
Central cavity
Yellow bone marrow
Fibrous
connective tissue
Blood vessels
Cartilage
Figure 27.28
Skeletal Diseases and Injuries
• The human skeleton
–
Is quite strong and provides reliable support, but
–
Is susceptible to disease and injury
• Arthritis
–
Is an inflammation of the joints
–
Affects one out of every seven people in the United States
• Rheumatoid arthritis
–
Is an autoimmune disease
–
Usually begins between ages 40 and 50
–
Affects more women than men
• Osteoporosis
–
Makes bones thinner and more porous
–
Is most common in women after menopause
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• Bones are rigid but not inflexible.
• If a force applied to a bone exceeds its capacity to bend, the
result is a broken bone or fracture.
• The treatment of a fracture involves
– Putting the bone back into its natural shape
– Immobilizing it until the body’s natural bone-building cells can repair the
fracture
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Figure 27.29
The Muscular System
• The muscular system is made of all the skeletal muscles in the
body.
• Skeletal muscles
– Are attached to the skeleton
– Pull on bones to produce movements
• Tendons connect muscles to bones.
• Antagonistic pairs of muscles produce opposite movements.
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Know this!
Biceps relaxed
Biceps
contracted
Triceps
relaxed
Tendon
Triceps
contracted
Figure 27.30
Muscle
Nuclei
Bundle of
muscle fibers
Single muscle fiber
(cell)
Myofibril
Light
band
Dark band
Light
band
TEM
Sarcomere
Thick
filaments
(myosin)
Light
band
Dark band
Light
band
Thin
filaments
(actin)
Sarcomere
Figure 27.31
• Each skeletal muscle cell, or fiber
– Contains bundles of myofibrils
– Is called striated, because the myofibrils exhibit alternating light and
dark bands when viewed with a light microscope
• A sarcomere
– Is the region between two dark, narrow lines called Z lines
– Is the functional unit of muscle contraction
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• A myofibril is composed of two kinds of filaments:
– Thin filaments, made mostly of the protein actin
– Thick filaments, made mostly of the protein myosin
• A sarcomere contracts when its thin filaments slide across its
thick filaments.
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Sarcomere
Dark band
Relaxed
muscle
Contracting
muscle
Fully
contracted
muscle
Figure 27.32
• In the sliding-filament model, the key events are the binding
between
– Parts (called heads) of the myosin molecules in the thick filaments
– Specific sites on actin molecules in the thin filaments
• Contraction requires energy supplied by ATP.
thick
thin
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Motor Neurons: Control of Muscle Contraction
• Motor neurons
– Can branch to a number of muscle fibers
– Stimulate muscles to contract
• A neuromuscular junction is the connection between
– A motor neuron
– Muscle fibers associated with that neuron
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• A motor unit consists of
– A neuron
– All the muscle fibers it controls
• Motor units may consist of
– Just one muscle fiber or
– Up to hundreds of muscle fibers
• The strength of a muscle contraction depends on the number of
motor units activated.
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Spinal cord
Motor
unit 1
Motor
unit 2
Nerve
Motor
neuron
cell body
Motor
neuron axon
Nuclei
Neuromuscular
junctions
Muscle fibers (cells)
Muscle
Tendon
Bone
Figure 27.34